Coining holographic images into contoured surfaces on hard temper metal products

ABSTRACT

A method for coining holographic images or holograms in a contoured or tapered surface of hard metal articles such as automotive products and sporting and fitness products including ball bats using a split die having an interior surface mirroring the contoured or tapered surface of the metal article.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to coining or microengraving holograms and/or diffraction images into contoured or tapered surfaces on metallic products such as ball bats.

[0003] 2. Description of the Prior Art

[0004] Many recreational and competitive softball and baseball players prefer to use ball bats made of hard temper aluminum alloys. There are two predominant methods for decorating baseball and softball bats: powder coating and anodizing. Both processes utilize silk screening as the primary method of applying decorative images and corporate logos to the painted or anodized aluminum. There is a need for improved and enhanced technology for decoration of ball bats and other metal products to improve their appeal.

[0005] There is also a need for improved techniques for manufacturers to authenticate their products such as ball bats to help prevent counterfeiting of these products. One way that manufacturers authenticate/identify their products is by applying an adhesive label, sometimes including holograms on the labels, that indicate that the products were made in their plants. These labels tend to fade and peel off the products over time, and are usually placed in areas on the products that take much abuse. The labels also can be expensive. Improved identification/authentication technology is needed which would withstand abuse and be more durable.

[0006] It is well known to manufacture a variety of products having holograms or diffraction images pressed or embossed into them. Such products include credit cards, license plates, consumer packaging, pictures, tickets and the like. See, for example, U.S. Pat. Nos. 4,368,979; 4,684,795; 4,856,857; 4,971,646; 4,999,075; and 5,267,753. Holograms generally mean a diffraction pattern which produces a three-dimensional image. Other diffraction images modify the behavior of light that strikes an object bearing the image without creating a three-dimensional appearance. The term “hologram” is used herein in the broad sense to include diffraction patterns or images as well as three-dimensional holograms and other complex images having different planes of diffraction. The manufacture of holograms, shims or plates is well known in the art as disclosed in Practical Holography, Graham Saxby (2d Edition, 1994) and U.S. Pat. Nos. 3,733,258; 3,875,026; 3,944,420; and 5,059,499, among others.

[0007] The creation of a master hologram is well known in the art. One common process (see U.S. Pat. No. 5,521,030 for example) is to apply a photosensitive coating (photoresist) to a substrate such as glass or metal and to etch the photoresist with two or more coherent beams of light (laser beams) to produce a surface relief pattern (hologram) with a depth corresponding to the intensity of the radiation at each point. The relief grooves or pits that are etched into the photoresist preferably have a maximum depth not greater than the thickness of the photoresist on the substrate. The photoresist preferably has a thickness of a least about 3 microns (120 microinches) in order to obtain relief grooves or pits in the hologram in the photoresist that are at least about 2 microns deep, and more preferably at least about 3 microns deep. The relief grooves may have an aspect ratio of depth to width in a range of about 1:0.5 to 3:1. The master hologram that is produced in the photoresist material is fragile and relatively soft.

[0008] The image in the photoresist of the master hologram is a “positive” image. As used herein, a “positive” image means the same image as is desired in the final object. A “negative” image is the inverse of a positive image, like the image in a mirror in which letters/words/images or other directional-sensitive decorations or patterns are reversed. The image in the master hologram is typically a positive image, but it could also be created as a negative image in the sense of any letters/words or other directional-sensitive images. If the image in the master hologram is created as a negative image with letters/words reversed, then the number of image transfers from master hologram to the final object will be changed by adding or subtracting an odd number of transfers so the letters/words on the final object will be positive. If there are no letters/words in the image, then it may not matter whether the image on the final object is positive or negative.

[0009] It is also well known in the art to grow a metal shim or mother shim from the master hologram. This can be done by applying a conductive coating (for example, silver spray) over the photoresist and then immersing the photoresist, i.e., the master hologram, in a bath of metal salts such as nickel salts and electrolytically growing or depositing nickel on the master hologram to generate a negative image of the hologram in a nickel shim. The image on the shim is the inverse of the image on the master hologram in that the grooves in the master hologram produce ridges or peaks on the shim, and also the reverse of the image on the master hologram. The thickness of the metal (nickel) shim varies depending on several factors such as the growing time used. The height of the ridges on or pits in the shim is the same or close to the same depth as the grooves or pits in the photoresist. After the nickel shim has grown to the desired thickness, it is peeled or stripped from the master hologram to expose the negative image in the surface of the mother shim.

[0010] The next step in the process is to create multiple shims from the mother shim. It is known in the art to produce 100 or more daughters of the mother shim. This is done by growing daughters of the mother shim (sister shims of each other) in a bath of metal salts in the same manner that the mother shim was grown on the master hologram as described above. In this way, many sister shims are grown. A negative image on the mother shim becomes a positive image on each of the sister shims. It is important that the surfaces of the mother shim and the sister shims be as smooth as possible to avoid pressing any imperfections from such surfaces into the hologram images made from the shims. It is also important that the undersurface of the sister shims be smooth. Since the shims are relatively thin, small blemishes on the undersurface of the shims or on surfaces on which the shims are mounted can be transferred through the shims into the holograms produced by the shims. The opposite faces or surfaces of the shim should be parallel, and the shim should have a uniform thickness within a tolerance of less than about 0.005 inch from edge-to-edge across the width of the shim.

[0011] When the sister shims are grown from the mother, the image on each of the sister shims is the inverse of the image on the mother shim. Thus, ridges or peaks on the mother shim will be grooves or pits in the sister shims. The depth of such grooves or pits is desirably as close to the height of the ridges or peaks on the mother image, but may be considerably less, such as only about 50% of the height of the ridges or peaks, as a result of the transfer process.

[0012] Most holograms on credit cards and the like are embossed into a plastic sheet material such as Mylar® or other polyester which has a thin underlayer of reflective material such as aluminum to produce a reflective hologram. The aluminum is typically vapor deposited onto the substrate. Holograms can also be impressed into thermoplastic layers on durable substrates as disclosed in U.S. Pat. No. 4,913,858. The coated sheet is heated to soften the coating which is decorated using an embossing member to provide a diffraction pattern or hologram.

[0013] It is further known to create embossing tools or roller dies bearing holographic patterns which are impressed into aluminum foil, translucent plastics and other materials, as is disclosed in U.S. Pat. No. 5,521,030. That patent discloses a process in which the holographic pattern is etched directly into a durable surface on the tool or die. The patent states that large quantities of holograms can be made from a single die made of high quality steel, chrome, or the like that is used in the roller die. The patent further states that the die may be a flat plate mounted on a substrate, an inside surface of an injection mold, a mandrel, a casting mold, or other surface used for transferring a relief pattern. The patent states that the holographic pattern may be embossed into aluminum foil, aluminum sheets, steel beverage containers, or the like. It is also known to emboss holograms directly into the outer surface of sheet metal such as aluminum foil and aluminum beverage cans as is disclosed in U.S. Pat. Nos. 4,773,718 and 4,725,111.

[0014] Another technique for forming a hologram or diffraction grating in a metal blank or a metal container is disclosed in U.S. Pat. No. 5,193,014. According to that patent, a hologram or diffraction grating is first formed on a gently curved surface of a metal plate mold, followed by stamping the metal blank or can with the plate mold to transfer the hologram.

[0015] Most processes for transferring holographic images to metal products are limited to flat or tubular products. This is because high pressures are required to affect the transfer and the difficulty of ensuring uniform or substantially equal transfer pressure between the shim or die and the metal surface to receive the image. Accordingly, most methods transfer the images from one planar surface to another planar surface, or from one cylindrical surface to another cylindrical surface as the two cylindrical surfaces are rotated against one another. The typical method for transferring images is a rolling method such as that described in U.S. Pat. Nos. 5,881,444 and 6,006,415.

[0016] The rolling process disclosed in U.S. Pat. Nos. 5,881,444 and 6,006,415 relies upon a continuous line contact where the tangent point on the print cylinder is brought into contact with the corresponding tangential section on a cylindrical can body. The line contact, called the contact patch, is in the range of 0.040-0.060 inch wide by 3.7-3.8 inches long for a conventional 12 oz. can. The forces that are generated during transfer to a can are concentrated in this contact patch area, and are continually shifting as the can and print cylinders rotate through the rolling process to achieve image transfer. Yielding of the metal surface was needed to achieve image transfer to the aluminum substrate. One of the advantages of the rolling process is that the dimensions of the tooling, and the tonnage of the press used, are kept small due to the size of the contact patch. As the area being embossed increases, the force (i.e., load) applied to the part being embossed has to increase to overcome the yield strength of the aluminum substrate into which the image is being transferred.

[0017] A method and apparatus is needed for transferring holographic images into non-planar and non-cylindrical surfaces such as the tapered portion of a ball bat or other metal products.

[0018] An improved, low-cost technique is desired for embossing holograms into metal sporting and fitness products such as ball bats, tubes for bicycle frames, rackets for tennis and the like, and exercise equipment. Many thousands of aluminum ball bats are made and sold annually, and improved decoration and authentication of such bats would improve their marketability. Aluminum sports products are frequently made from hard temper aluminum alloys which provide high strength and durability for the products. It is important that the temper and strength of aluminum ball bats not be unduly reduced during processing as might happen if the bats are heated.

[0019] A technique for embossing or engraving holograms on metal into tapered surfaces of metal products such as ball bats is needed which adds little to the cost of the products and which produces consistently high quality images. It is desirable for a manufacturing system to be capable of engraving/embossing holograms on thousands of products in order to be commercially practicable. Sporting goods companies demand high quality and will not accept noticeable variations in the decoration on their products. The decoration processes must also be statistically in control and capable at such speeds.

SUMMARY OF THE INVENTION

[0020] The present invention meets the above-described needs by providing a process for decorating and authenticating tapered surfaces on thousands of ball bats or other high quality aluminum sporting and fitness products. The cost of decorating aluminum sporting and fitness products by this invention is nominal and is economical for mass marketing of the products. This invention can be used for decorating tapered or curved surfaces on a variety of metal products such as ball bats, rackets for tennis and the like, tubes for bicycle frames, exercise equipment and the like. The tapered portion of most ball bats has a curved, frustoconical surface for receiving the hologram. This invention can also be used to transfer holograms to a variety of other products having non-planar, curved or contoured surfaces which may be symmetrical or asymmetrical and/or of uniform or non-uniform contour/curve(s). The surfaces can be concave as well as convex, and may also be rounded, arched or bowed. The products are preferably made of hard temper aluminum but may also be made of steel, stainless steel or other hard temper metals.

[0021] This invention uses a nickel shim having a holographic pattern in it to decorate the metallic products. The shim must have sufficient surface hardness to transfer a holographic image into hard sheet metal. The nickel shim should have a hardness of at least about 2.5 times the hardness of the article to which the image is to be transferred.

[0022] The surface of the shims is hardened for example by putting an amorphous diamond coating (ADC) or a diamond-like coating (DLC) on them. The coating is very thin and of uniform thickness to minimize possible adverse effect on the clarity of the holographic pattern, while being thick enough to provide the requisite hardness for engraving/embossing many thousands of ball bats or other metal articles.

[0023] It is an object of this invention to provide a method for coining/engraving/embossing holograms into the exterior tapered or curved surface of hard metal articles including sporting and fitness products such as ball bats, tubes for bicycle frames, sports rackets and exercise equipment, automotive and motorcycle products such as wheels and gas tanks, and other industrial and consumer products.

[0024] Another object of this invention is to provide a method for economically engraving/embossing holograms having uniformity and clarity into contoured surfaces of many thousands of metal products with the same dies.

[0025] It is also an object of this invention to provide improved dies for engraving/embossing holograms into sporting and fitness products made of hard metal.

[0026] A further object is to provide a method and apparatus for decorating metal products with holograms and decorative coatings at high speeds for mass production of aluminum products without adversely affecting the mechanical properties of the products.

[0027] Another object is to provide improved hologram-decorated products made of hard temper aluminum.

[0028] The above and other objects and advantages of this invention will be more fully understood and appreciated with reference to the attached drawings and the following description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a cross-sectional view through a ball bat suitable to be coined with a graphic image in accordance with this invention.

[0030]FIG. 2 is an end view of split clamshell dies suitable for use to decorate/emboss bats in accordance with this invention.

[0031]FIG. 3 is a side elevational view of the dies of FIG. 2.

[0032]FIG. 4 is a cross-sectional view of a ball bat with a mandrel positioned in it in preparation for coining a holographic image on the surface of the bat.

[0033]FIG. 5 is a side elevational view showing a ball bat in the dies of FIGS. 2 and 3 preparatory to coining/embossing holograms into the surface of the tapered portion of a ball bat.

[0034]FIG. 6 is a fragmentary perspective view of a ball bat that has been decorated/embossed with a hologram in accordance with this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] According to the present invention, hard metal articles such as automotive products, bats and tubes for bicycle frames and other sporting and fitness products have holographic images or holograms coined or microengraved in their surfaces by a die or dies having the negative of the images impressed in their surfaces. The objects that are decorated/embossed in accordance with this invention are preferably made of hard temper aluminum alloys such as 3000, 5000, 6000, 7000 and 8000 series aluminum alloys. In the case of aluminum ball bats, the bats are made by a variety of techniques, such as swaging a cylindrical extrusion or tube as disclosed by U.S. Pat. No. 3,854,316, rolling a portion of an aluminum tube to reduce its diameter as disclosed by U.S. Pat. No. 5,125,251, or reforming an aluminum tube as disclosed by U.S. Pat. No. 5,626,050, the disclosure of which is incorporated herein by reference. Bats produced by such processing usually have a barrel portion, a handle section, and a tapered section connecting the barrel section and handle section. The wall thicknesses of the three portions are different, with the thickness of the barrel portion typically being the same as the original thickness of the tube. The tapered portion and handle portion of the bat typically have thicker walls.

[0036] As used herein, the terms “coin”, “engrave”, “emboss”, “transfer” and “impress” mean the transfer of a holographic or a diffraction image from one article or tool to another article or tool by pressing the articles, shims or dies against one another under high pressure. The images are in the form of very small grooves (plane grating) or pits (dot matrix) in or on the surface of the objects. The transfer is into the outer surface of the tools and articles. This invention preferably uses dot matrix holograms which consist of millions of tiny diffraction grating, or “holopixels” oriented at different angles and arranged in a two-dimensional array. When illuminated with white light, the holopixels break up the light into a spectrum of colors and redirect the light at various angles to form a kinetic holographic image.

[0037] Ball bats, sports rackets and aluminum tubes and extrusions for the manufacture of bicycle frames, automotive wheels and the like, which are engraved/embossed in accordance with this invention, preferably have high specularity or brightness in order to produce the desired clarity of the hologram in the surface of the article. This means that the metal products preferably have a substantially mirror-like surface characterized by having a high distinctness of reflected image (“D/I” for brevity). When a ball bat or other product having a high D/I is positioned adjacent an article or an image or printing on paper or the like, the image or reflection on the bat or other metal product should be clear. D/I is the sharpness of the reflected image, and is preferably in a range of at least about 50 to 70% for products to be engraved/embossed by the method of this invention. High specularity can be produced on the bats, tubular metal and other products in a variety of ways such as burnishing or buffing the exterior surfaces of the bats and other products or by chemically cleaning and etching them. However, bat and tube makers may be able to produce products having specularity levels, after being washed, which may be high enough for transfer of holograms to the products without further brightening. Most ball bats produced commercially today are polished after they have been formed and before the ends are plugged or otherwise closed. In accordance with this invention, the bats are preferably coined to form a holographic image therein after such polishing and before the ends are closed.

[0038] The manufacture of shims and/or dies having holographic images on them is well known in the art, as is described in U.S. Pat. No. 6,006,415, the disclosure of which is incorporated herein by reference.

[0039] The shims used to stamp holographic images into curved or tapered surfaces of metal articles in accordance with this invention are preferably electroformed in a hardening bath to produce enhanced hardness and durability, and/or have a hard surface coating applied to them. The use of a hardening bath is disclosed in U.S. Pat. No. 6,017,657. The nickel can also be hardened by ion implantation with a nitrogen plasma. The hologram surface can be coated with a thin diamond-like carbon (DLC) coating or amorphous diamond coating (ADC) or diamond-like carbon films or carbon nitride coatings. The coatings or films may be formed on the surface of the shims by high temperature chemical vapor deposition (CVD) or enhanced cathodic-arc physical vapor deposition processes that create a high energy flux of carbon ions that are caused to be embedded in the surface of the shim. DLC coatings can also be applied by low temperature physical vapor deposition (PVD) such as cathodic arc deposition of the coating. The physical and mechanical properties of the shim substrate remain substantially unaffected by the coating process, but the coating on the surface has a hardness approaching that of natural diamond. The coating is tightly bonded to the shim substrate and is abrasion resistant. Due to the amorphous nature of the ADC, it requires no post-coat polishing. The coating is continuous and homogeneous and substantially exactly replicates the underlying surface so it does not noticeably degrade the topography of the hologram image. The Tetrabond® Division of Multi-Arc Inc. in Rockaway, N.J. applies TETRABOND® coatings or other similar coatings on a variety of products for various uses and also supplies equipment for applying such coatings.

[0040] It is known that ADC coatings or films may contain high levels of compressive stress. It is believed that the stress levels may be reduced by using a newly developed coating process that uses a pulsed laser on a graphite target at room temperature to produce a high percentage of diamond-like bonds. The coating so produced initially has a high stress level, but heating the coating reduces its stress while retaining its diamond-like properties. The resultant coating is reportedly extremely smooth and more stable than typical diamond films that contain hydrogen. It has been reported that Sandia National Laboratory has filed for a patent on this new process.

[0041] The ADC or DLC coating or film is preferably less than about 5000 angstroms thick in order to minimize masking or dulling of the hologram in the surface. ADC coatings may have hardness in a range of about 80-100 Gpa (giga pascal) (8,000-10,000 Vickers), be optically smooth and have a high adherence to the shim substrate. DLC coatings may have hardness in a range of about 10-50 Gpa (1,000-5,000 Vickers). The Gpa hardness measure is used by Multi-Arc Inc., whereas Knoop Microhardness (KHN) is measured in terms of kg/mm² (kilograms per square millimeter). KHN is used below to describe the hardness of shims, dies and ball bats. Vickers and Rockwell hardness can also be used to measure surface hardness. One kg/mm² is the equivalent of one Newton/mm² in the meter-kilogram-second system. Hardness measurements depend on the nature and size of the indenters, and there are no generally accepted conversion factors from one unit of measurement to another.

[0042] The sister shims preferably have a surface hardness of approximately 550-600 kg/mm² (500-600 KHN), regardless of whether their surface has been hardened or hard coated as described above. It is important to provide a sufficient hard surface hardness on the shims to affect a transfer of the hologram image into the surface of a ball bat in the next step of the process. It is preferred that effective transfer of a hologram image from the shim to the ball bat employ a hardness ratio of the two surfaces of at least about 2.5 to 1 and preferably at least about 2.7 to 1. This means that the surface from which the image is being transferred should be at least about 2.5 times, and preferably at least 4 to 5, harder than the surface into which the image is being impressed.

[0043] In a preferred mode of practicing the invention, one or more sister shims are preferably laminated to the surface of a support die. Alternatively, the holographic image on a sister shim can be transferred into the surface of a die, which is then used to coin the hologram into the ball bats or other articles. The dies are preferably made of aluminum, steel or other hard metal, and are more preferably made from an aluminum alloy such as 6061, 7075 or other 6000 and 7000 series aluminum alloys, or steel alloys such as 4140, 1018, 1045 and mold steel alloys, and have surface hardnesses of about 110-125 kg/mm². Dies made of 2024 or 4045 aluminum alloys, or other lower yield strength aluminum alloys or other softer, lower strength metals, may also be suitable for some applications. However, dies made of higher yield strength alloys, such as 7075 aluminum alloy and 4140, 1018, 1045 and mold steel alloys, appear to be more robust and capable of more cycles of operation than dies made of lower yield strength alloys. The dies may also be steel or other metal, with or without metalized coatings, such as metalized aluminum, on them.

[0044] If the holographic image is transferred to the die, then the dies are hardened. This can be done by ion implantation or by coating the dies with ADC or DLC as described above with reference to the sister shims. The ADC or DLC is also believed to be beneficial to reducing oxide or other scum build-up on the dies when they are used to emboss ball bats as described below. The surfaces of the dies preferably have a minimum hardness of at least 545 to 600 kg/mm² (or 545-600 KHN) after they have been hardened. The surfaces of the dies should be at least 2.5 times, and preferably at least about 4 to 5 times, harder than the surface hardness of aluminum sports products to be decorated. Aluminum bats and other sports products have tensile yield strengths (TYS) of about 85 ksi and Knoop Microhardness of about 200. A surface hardness of at least about 500 kg/mm² (or 500 KHN) on the dies is required to make a good transfer of the image into the surface of the products. For softer products, the dies may have a lower surface hardness.

[0045]FIG. 1 shows a typical partially formed ball bat 10 that is suitable for decoration and/or authentication in accordance with this invention. The bat 10 is preferably made of a hard temper aluminum alloy but may also be made of steel. The bat 10 has handle end 12, a barrel end 14 and a tapered portion 16 connecting the handle and the barrel ends of the bat. The bat 10 of FIG. 1 is hollow throughout its length since the ends have not been closed by plugs or metalforming as is well known in the art. The handle end 12 will have a knob, not shown, provided thereon, and the barrel end 14 will be closed after that bat is decorated or authenticated in accordance with this invention.

[0046] Several different aluminum alloys are typically used in baseball bats, including 7046, C405, C55 and C805. C405, for example, has a tensile yield strength (TYS) of about 85 ksi and a KHN of about 200.

[0047]FIGS. 2 and 3 show a developmental/laboratory split die 20 for microengraving a ball bat 10 in accordance with this invention. The die 20 includes a lower die half 22 and an upper die half 24 having stamping surfaces 26 and 28 on them which mirror the tapered portion 16 of the bat 10. The die 20 further has mounting plates 30 and 32 on the two halves for securing them in a press, not shown, for moving at least one of the two halves linearly toward and away from the other to open and close the die. The lower die half 22 preferably has a plurality of upwardly projecting guide pins 34 on it that mate with guide holes 36 in the upper die half 24 to help ensure proper alignment of the two die halves during closing of the die.

[0048] In a preferred embodiment of the die 20 for commercial practice of this invention, the shims 40 and 42 would be laminated to the tapered surfaces 26 and 28 of the die halves 22 and 24. Alternatively, only one shim might be laminated to one of the die halves 22 and 24. As described above, the shims 40, 42 have holographic images on them to be microengraved in the tapered surface of the bat. It is important that the die 20 and shims 40, 42 mirror the taper and curvature of the bat surface so the shims can be pressed against the bat surface with substantially uniform pressure of the shims against the bat surfaces for the entire surface area of the shims.

[0049] Each shim 40, 42 having a hologram image on it is preferably sized to correspond to the size of the surface area of the bats to be coined/embossed. For example, in one developmental setup for practicing the invention, holographic images were transferred into approximately a 3-inch length of the tapered portion 16 of several bats where the tapered portion went from about a 2-inch circumference to about a 3-inch circumference, and two rectangular shims approximately 3 inches long and 1.5 inches wide were used. However, the diameter, length and shape of the shims are not critical to this invention. For example, the shims could be of a variety of sizes and could also be tapered in width corresponding to the progressively increasing circumference of the tapered portion of the bats.

[0050]FIG. 4 shows a ball bat 10 with a mandrel 44 positioned in the tapered portion 16 of the bat to support the wall of the bat during coining of a holographic image into the outer surface of the tapered portion in a developmental laboratory. The mandrel 44 is held in position by a rod 46, a disc-shaped clevis 48 and a nut 50. The rod 46 has one end tightly secured in or to the mandrel 44 and has its opposite end threaded to receive the nut 50. The clevis 48 shaped like a wheel or pulley and is designed to fit in a mating bracket on the tools shown in FIG. 5 as is described below. At least one and preferably several washers 52 are disposed between the clevis 48 and the end of the bat 10. The mandrel 44 is preferably pulled tightly against the interior of the tapered portion 16 of the bat by tightening the nut 50 on rod 46.

[0051]FIG. 5 shows a ball bat 10 secured in a laboratory press 54 in preparation for coining a holographic image into its tapered surface. The press has an arm rigidly secured to lower platen 58 and has a bracket 60 secured on its end for receiving the clevis 48 on the end of the rod 46. The bracket 60 projects upwardly from arm 56 and has an upwardly open U-shaped slot (not shown) in it in which the clevis 48 fits to restrain the clevis 48, rod 46, mandrel 44 and bat 10 against movement along the axis of the rod and bat.

[0052] As shown in FIG. 5, the bat 10 is seated in the lower die half 22. The bracket 60 is positioned so that the tapered portion 16 of the bat 10 fits snugly against the tapered surface on the lower die half 22. This fit depends on the length of the bat handle 12 and the relative position of the clevis 48 on the rod 46 and the bracket 60 on arm 56. The number and/or thickness of the washers 52 between the clevis 48 and the end of the bat can be varied to adjust the longitudinal position of the bat and assure a snug fit of the tapered surfaces of the bat 10 and lower die half 22. This snug fit is desired to provide optimum transfer of the holographic image from the die/shims into the surface of the ball bat 10.

[0053] Following positioning of the ball bat 10 in the press 54 as shown in FIG. 5, the die halves are closed with respect to one another to press the two die halves against the tapered portion of the bat. The press used in the development laboratory is a 45-ton Bliss press. It is desirable, but not critical, for the die to impact against the surface of the bat 10 to enhance transfer of the hologram into the surface of the bat.

[0054] In the laboratory setup, the shims 40, 42 were not laminated to the die halves 22, 24. Instead, the shim 40 was placed unsecured in position in the lower die half 22, and the shim 42 was placed unsecured on the top of the barrel portion 16 of the bat 10. In some cases, the shims 40, 42 were initially flat before the first bat 10 was coined, and were reformed into the curved shape of the bat during the coining of the bat. This curved shape of the shims 40, 42 then facilitated positioning of the shims in the dies for coining additional bats. In some cases, especially when using relatively thick shims of more than 0.005-0.010 inch in thickness, the shims were preferably at least partially preformed into a curved configuration like the tapered portion of the bats before the first bat was coined. In a commercial transfer of holograms to bats, curved shims would preferably be permanently laminated to the die halves. Such lamination could be made with an adhesive, double stick tape or other lamination technique. The dies may also be undercut to provide seats in which the shims would fit. The undercut would be shallower than the thickness of the shims so the shims would project slightly above the surface of the dies.

[0055] Since the shims project above the surface of the die halves 22, 24, the full force of the press against the bat is carried by the shims. The unit pressure of the shim against the bat is thus several thousand pounds per square inch. For example, a 45-ton press would theoretically apply approximately 10,000 psi of pressure of a four (4) inch² shim against the surface of the ball bat. The edges of the shims are preferably rounded in order to minimize gouging or digging of the edges of the shims into the bat.

[0056] As stated above, the shims or dies should have a hardness of at least about 2.5 to 3 times the surface hardness of the bat. The shims are pressed against the surface of the bat 10. The pressure of the shim against the bat surface is preferably about 1500 to 2000 pounds per square inch of contact at the bat/shim interface. The pressure must be sufficient to microengrave/emboss the holographic image from the shim into the surface of the bat, but should not be so high as to significantly extrude metal in the wall of the bat from between the shims 40, 42 and the mandrel 44. Extrusion of metal in the wall of the bat causes minimal thinning of the wall and may deform the bat slightly. However, a small amount of metalworking and thinning of the wall is acceptable. Such metalworking may result in slight changes in the circumference of the barrel of the bat and a slight increase in the strength of the bat in the area of the metalworking. The bats or other sporting products are preferably at room temperature during transfer of the holographic image into the surface of the products.

[0057] For high volume production of aluminum bats and other hard metal products, it may be beneficial to apply a lubricant on the surface of the shims or the metal products during transfer of the image from the shims to the product. The lubricant may be applied to shims shown in FIGS. 2 and 3 or to the bats 30 before the shims are pressed against the bats. The lubricant may help reduce the pick up of aluminum oxide or other debris during transfer of the image to the bat and may also help remove any metal fines or debris which are produced from the surface of the shims. Metal fines and/or other debris that may accumulate on the surface of the shims may interfere with transfer of the image to the bats, particularly if the same shim is used to decorate many thousands of bats. The fines and debris tend to blind the shims or make them less effective in impressing the holographic image into the surface of the bats or other articles. In a preferred embodiment, the lubricant may be sprayed intermittently on the shims. It may be desirable to periodically wipe or otherwise clean the shims or dies in any production operation in order to maintain a robust system to produce high quality holograms in the bats or other articles. The cleaning solution might, for example, be a dilute solution (2%) of a body forming lubricant (aluminum can bodies) and water.

[0058] It is believed that a variety of lubricants or boundary additives to lubricants may be used on the die or bats including fatty acids, fatty alcohols and esters, including oleic acid, stearic acid, methyl stearate and butyl stearate. The quantity of lubricant should be controlled to avoid possible detrimental effects on the bats. For example, excessive quantities of some lubricants may cause dulling or cloudiness on the surface of the bats. It is therefore desirable to carefully meter the lubricant onto the dies and/or bats, or ineffective transfer of the holographic image from the tool to the bat may occur.

[0059] Ball bats and other sporting and fitness products which are decorated and/or authenticated in accordance with this invention are preferably also decorated and/or colored with a powder coating or by anodizing the surfaces of the products. Both such processes use silk-screening as the primary method for decorating/coloring the products. Such decorating/coloring may be done either before or after the sporting product has been microengraved with a holographic image in accordance with this invention. The anodizing may include the entire bat or alternatively the hologram image may be masked before the bat is anodized. An over-varnish may also be applied to the bat after the hologram has been coined in its surface.

[0060] It is noted that the combination of a holographic image and decorative coatings on a bat produces an extremely attractive bat. The decorative coating may be applied only to the surface of the bat which does not include the hologram, or may also be applied over all or part of the hologram. The hologram and decorative coating interact to produce an appearance not previously possible in the manufacture of bats.

EXAMPLE

[0061]FIG. 5 shows one example of an aluminum ball bat that had been decorated by the method of this invention having a hologram comprising pictures of bats, balls and stars coined in or embossed on its surface. The light which reflects off the hologram produces varying looks or images as the bat is moved in the light. The hologram image has been transferred to the tapered portion only of the bat. However, this invention may also be used to transfer holographic images to the barrel or handle portions of the bat.

[0062] The shims in the method of FIGS. 3 and 4 have negative holographic images on them and press a positive image in the exterior surface of bats. The image in the photoresist material preferably comprises pits (dot matrix), the image on the mother shim comprises peaks (dot matrix), the images on the sister shims comprise pits, and the images in the surface of the bats comprise peaks. It is important to the method of FIGS. 3 and 4 that the shims have a surface hardness of at least about 500 to 650 kg/mm² (or 500-650 KHN) in order to effectively press a hologram into the surface of aluminum bats having surface hardness of about 150 to 200 kg/mm² (or 150-200 KHN). The surface of the shims may be optionally hardened with DLC or ADC as is described above with respect to the method of FIG. 1.

[0063] Whereas particular embodiments of this invention have been described for purposes of illustration, it will be evident to those skilled in the art that numerous variations in details may be made without departing from the invention as covered by the appended claims. For example, the method of this invention can be used to emboss/engrave holograms on a variety of products such as sports rackets, tubes for bicycle frames and other articles of manufacture. Some such products may have surface hardnesses in a range of about 100 to 200 kg/mm² (or 100-200 KHN). It is also possible to modify this invention by first transferring the hologram to a die or dies that are used to coin the hologram into the surface of the bat(s).

[0064] Shims used with this invention may also be prestressed or alternatively stress relieved to reduce squirming or movement of the edges of the shims during transfer of images to a ball bat or other objects.

[0065] The ADC or DLC coatings on the shims and/or dies may also vary in thickness down to about 1,000 angstroms, although they are preferably about 2,000-3,000 angstroms thick. The products that may be decorated in accordance with this invention may also have a thin, clear coating of polymer such as polyester on them, and the holographic image may be transferred to such coating that is similar to image transfer to credit cards or the like, although with less clarity of the image as compared with transfer of images into bare metal. Although the invention has been described in terms of forming images on ball bats, the invention is not intended to be so limited. It is contemplated that the invention will be especially useful for a variety of products such as sporting products including lacrosse sticks, hockey sticks, polo sticks, wind surfing frames, sail board booms, inline skate components, wheelchairs, golf clubs, motorcycle and bicycle frames and components (handlebars, seat, posts, suspension systems), ski poles, javelins, bowling pins and automotive products such as wheels and tool boxes, and other consumer and industrial products. 

We claim:
 1. A method for coining a holographic image in at least a portion of a tapered surface of a hollow, hard temper metal article comprising: providing a hollow, hard temper metal article having a tapered, bright finish surface on it for receiving a holographic image; inserting a solid mandrel into the metal article to support at least a portion thereof to receive the holographic image; providing a split die having an internal shape substantially mirroring the shape of said portion of the metal article and having a dot matrix type holographic image on at least a portion of the interior surface thereof for coining the surface of said metal article, with the surface of the die having the holographic image thereon having a surface hardness of at least about 400 KHN, said split die having two parts moveable linearly to open and close the die; securing said metal article to minimize movement thereof during transfer of the holographic image; and closing said split die against the tapered surface of the metal article to coin the holographic image into at least a portion of the tapered surface.
 2. The method as set forth in claim 1 in which said split die has at least one shim in the die with the holographic image on the shim.
 3. The method as set forth in claim 1 in which said metal article is an aluminum ball bat having a tapered portion which is coined by said method.
 4. The method as set forth in claim 1 in which the surface hardness of said die is at least 500 KHN.
 5. The method as set forth in claim 1 in which said mandrel is a hardened steel mandrel.
 6. The method as set forth in claim 2 in which each of said parts of said split die has at least one shim in it.
 7. The method as set forth in claim 1 in which the tapered surface of said article has a D/I of at least 50%.
 8. The method as set forth in claim 1 in which the surface of said split die bearing said holographic image has a diamond-like coating thereon.
 9. The method as set forth in claim 3 in which said bat is secured against movement.
 10. The method as set forth in claim 3 in which said tapered portion of said ball bat is substantially frustoconical.
 11. An aluminum ball bat that has been coined by the method of claim
 1. 12. A method for coining a holographic image in at least a portion of a curved surface of a hollow, hard temper aluminum alloy ball bat comprising: inserting a hard temper steel mandrel into said ball bat to support at least the curved portion thereof to be coined; securing said ball bat against movement thereof during coining; providing a split die having two parts moveable linearly toward one another to open and close the die, said die having a curved internal shape substantially mirroring the shape of said curved portion of said ball bat and having a dot matrix type holographic image on at least a portion of the interior surface thereof for coining the surface of said metal article, with the surface of the die having the holographic image thereon having a surface hardness of at least about 500 KHN; and closing said split die against said curved surface of said ball bat to coin the holographic image into at least a portion of the curved surface of said ball bat.
 13. The method as set forth in claim 12 in which said split die has a shim bearing a holographic image in each of said parts of said die.
 14. The method as set forth in claim 13 in which each said shim is laminated to said die.
 15. The method as set forth in claim 13 in which each said shim has a diamond-like coating on it.
 16. The method as set forth in claim 12 in which said curved surface of said ball bat has a D/I of at least 50%.
 17. The method as set forth in claim 15 in which said coating has a thickness of not greater than 5000 angstroms.
 18. An aluminum ball bat that has been coined by the method of claim
 12. 19. An aluminum ball bat that has been coined by the method of claim
 15. 20. A method for coining a holographic image in at least a portion of a contoured surface of a hard metal article comprising: providing a hard metal article having a contoured surface on it to be coined, said contoured surface having a D/I of at least 50%; providing a die having a stamping surface on it bearing a holographic image to be coined into the contoured surface of said article, said stamping surface having a shape mirroring the contoured shape of said article and having a diamond-like coating on it with a hardness of at least 500 KHN; supporting said metal article against movement; and stamping said contoured surface of said article with said die to coin said holographic image into said contoured surface.
 21. The method as set forth in claim 20 in which said article is hollow, and a hard metal mandrel is positioned in it prior to said stamping to support the contoured surface during said stamping. 